The present invention relates to apparatus for forming and transferring thin films of ink, adhesive paste or other liquids. More particularly, the invention relates to improvements in apparatus wherein a continuous layer of liquid is being withdrawn from a vessel by a rotary member known as a fountain roll. Still more particularly, the invention relates to improvements in apparatus which can be used with particular advantage in tobacco processing machines for the application of thin films of a liquid to webs of cigarette paper, to blanks which are employed for the making of packs for cigarettes or the like, to strips which are to form adhesive-coated uniting bands, or the like.
As a rule, an apparatus which is to form a thin film of ink, adhesive or other liquid material comprises a vessel or tank which contains a supply of liquid and supports the shaft of a roll a portion of which dips into the supply of liquid so that the periphery of the roll withdraws from the supply a continuous layer of liquid. The layer is equalized by the blade of a preferably adjustable doctor whereby that portion of the liquid layer which is permitted to advance beyond the blade forms a film of desired thickness. If the liquid is an adhesive, the film can be applied directly to a web of cigarette paper or the like, or the film can be transferred onto one or more intermediate rolls before it comes into contact with a portion of or the entire side of a running web. If the liquid contains coloring matter, it is normally transferred onto one or more indicia-bearing imprinting members which are caused to move into contact with selected portions of a running web or with selected portions of blanks for the making of cigarette packs or the like.
A drawback of many presently known apparatus which form and transfer films of adhesive paste, ink or other liquids is that the liquid is permitted to escape from the tank, either along the fountain roll, along the doctor or along the fountain roll and the doctor. In most instances, the liquid can reach the ends of and thereupon drips from the fountain roll to thereby contaminate the apparatus as well as the machine wherein the apparatus is installed. Moreover, liquid which reaches the ends of the fountain roll is likely to form a crust on the shaft for the fountain roll, to penetrate into the bearings for the shaft, to contaminate the drive means which rotate the fountain roll, and/or to evaporate into the surrounding area. The drawbacks of hardened crusts of adhesive on gears, shafts, bearings and analogous parts will be readily apparent; however, inks and other liquids having a relatively low viscosity are also likely to create serious problems if they are free to escape from the vessel. Moreover, the liquids which are used in machines for the processing of tobacco, filter material, packs for cigarettes, cigars or cigarillos and/or other smokers' products are rather expensive so that it is obviously quite desirable to avoid unnecessary wasting of liquids in such machines.